Human umbilical cord epithelial cells express Notch1: Implications for its epidermal-like differentiation

Background: Notch1 receptor, a member of the Notch signaling pathway, is involved in the terminal differentiation process of epidermal keratinocytes. Human umbilical cord epithelia are continuous with embryonic and fetal epidermis during development, display cellular stratification and express differentiation markers related to the epidermis. As such, we hypothesized that Notch1 may be present in human umbilical cord epithelial cells (HUCEC). Objective: To investigate the expression of Notch1 in HUCEC in vivo and in vitro. Methods: Umbilical cord sections were probed with antibodies specific for Notch1, -2, -3, and -4. Expression of Notch transcripts in HUCEC in vitro was examined by RT-PCR analysis and protein expression was identified using immunocytochemistry and western blotting analysis. Using a three-dimensional organotypic culture system that promotes epidermal terminal differentiation, Notch1 expression was examined and changes in expression level were analysed using real-time quantitative PCR. Results: Immunostaining of cord epithelia revealed expression of all four Notch receptors, with differential spatial distribution. Notch mRNA and protein were expressed in HUCEC in vitro. Specifically, western blotting revealed the presence of the transmembrane unit of the mature Notch1 heterodimeric receptor in HUCEC and epidermal keratinocytes. In organotypic culture, Notch1 mRNA was expressed in HUCEC with protein localised to the upper epithelial layers. Interestingly, Notch1 gene expression was down-regulated in HUCEC in organotypic culture compared to cells in submerged monolayer culture. Conclusion: HUCEC express Notch1 as in epidermal keratinocytes. The presence of Notch1 has implications for its involvement in the differentiation program of cord epithelia as a stratified epithelial tissue.